A San Rafael automotive manager charged with insurance fraud was acquitted by a jury in Marin Superior Court.

Tommy Frederick Johnston, 64, was facing a potential three-year prison sentence and a felony record if he was convicted, but he refused to accept a plea deal for a lighter charge.

"I knew I was innocent," said Johnston, who lives in San Anselmo. "All I did was do an estimate for a guy who asked for an estimate."

The case stemmed from a series of sting operations in 2011 by the state Department of Insurance and auto-crime investigators with the Marin County Major Crimes Task Force. The intention of such stings is to find auto technicians willing to submit false claims to insurance companies for jobs.

On March 9, 2011, an undercover detective asked Johnston for an estimate to repaint his car. The decoy also told Johnston he had filed a false police report claiming the car had been scratched and dented, according to court filings.

"(The detective) explained to defendant that the vehicle had actually sustained no damage, but that he was claiming his car had been vandalized to get the insurance company to pay for his paint job," prosecutor Tom McCallister wrote.

Johnston inspected the car and faxed an estimate to Nationwide Insurance Co., saying the insurer was responsible for the repairs and the repainting, authorities said.

Prosecutors charged Johnston with supporting a fraudulent insurance claim. He was one of three estimators to be charged after stings at 29 Marin County auto shops in 2011, according to the district attorney's office.

Two of the estimators settled their cases with plea bargains. Johnston — who took a similar plea deal during the last round of stings, in 2005 — decided to take the case to trial.

The defense attorney who took his case, Robert Casper in San Rafael, argued that insurance companies investigate all damage claims, and Johnston knew as much. Casper also argued that there's only about a 30 percent chance that a customer will get repairs done at the same shop that did the estimate.

"My client did not intend to defraud anyone, as he was aware that any estimate he wrote would have to be verified," Casper said.

The four-day trial was held this month, with Johnston taking the stand himself. Late Friday afternoon, the jury acquitted him after about two hours of deliberation.

Johnston said he "almost collapsed" from the tension while waiting for the clerk to read the verdict.

Johnston, who has been doing auto repairs in Marin since 1988, said the prosecution appears to have a vendetta against auto body shops and estimators. He said cases like his are a waste of taxpayer funds.

District Attorney Ed Berberian disagreed, saying insurance fraud costs the public millions of dollars in increased premiums. He said going after offenders is worth the allocation of resources.

During the last wave of stings in 2005, Berberian said, authorities investigated 34 shops and, out of those, prosecuted 15 fraud cases, most or all of which resulted in guilty pleas.

"This is just one case," he said. "When you look at all the cases, this is one case that resulted in an acquittal."

At the time Johnston was charged, he worked for Bertolli's Auto Body in San Rafael, but he has since changed jobs. His former boss, Laura Bertolli, said she had another employee snagged — by a "flirtatious" female decoy — during the stings in 2005.